As a related art of the present invention, a pressure proportional control valve is known. This pressure proportional control valve is a constitution as shown in FIG. 5 (e.g. Japanese Unexamined Patent Publication No. 2004-197858 (Patent Document 1)). This pressure proportional control valve is a three-way valve used for, for example, a drive unit of an AT (automatic transmission) car and hydraulic control system.
The constitution of this pressure proportional control valve will be explained. In FIG. 5, a pressure proportional control valve 100 is constituted by a valve main body 101 and a solenoid 150. A main body 102 forming a framework of the valve main body 101 is internally formed with a communication chamber 103. The communication chamber 103 is formed with an input port 105, an output port 106 and a discharge port 107, which communicate with the outside. Also, the communication chamber 103 is divided into a first communication chamber 103A which communicates with the input port 105 and a second communication chamber 103B which communicates with the output port 106, by a partition plate 110. At the center of the partition plate 110, a first valve bore surrounding surface 110A is formed. At the side of the first communication chamber 103A in this first valve bore surrounding surface 110A, a first valve seating surface 110B is formed. Also, at the side of the second communication chamber 103B in the first valve bore surrounding surface 110A, a plurality of passage grooves 110C are partially formed along the surrounding surface. This passage groove 110C works together with a minor diameter surface of a first valve body 120 as a fluid passage, where a working fluid runs, when a first valve surface 120A of the first valve body 120 moves away from the first valve seating surface 110B to open.
Also, in the main body 102, a first pressure chamber 108 is formed between the first communication chamber 103A and the discharge port 107. This first pressure chamber 108 is provided with a first sliding surrounding surface 108A. This first sliding surrounding surface 108A is provided with a first annular groove to fit a first seal ring S1 in. Further, in the main body 102, a second pressure chamber 109 is formed to communicate with the second communication chamber 103B. An outer circumference of the second pressure chamber 109 is provided with a second sliding surrounding surface 109A. This second sliding surrounding surface 109A is provided with a second annular groove to fit a second seal ring S2 in.
Also, the first valve body 120 provided with an outer circumference surface 120C, movably fitted with the first sliding surrounding surface 108A of the main body 102 and the first valve bore surrounding surface 110A of the partition plate 110, is arranged. An axis of the first valve body 120 is provided with a communication passage 120D communicating with the first pressure chamber 108 and second pressure chamber 109. Also, this first valve body 120 is elastically pressed to the side of a second valve body 125 by a first spring 140A arranged in the first pressure chamber 108. Also, the first valve body 120 is provided with the first valve surface 120A at the intermediate part as well as the second valve surface 120B at the apical end. Also, a second spring 140B is arranged between the first valve body 120 and second valve body 125, and the first valve body 120 and the second valve body 125 are elastically pressed by the second spring 140B in opposing direction.
Further, the second valve body 125 movably fitted with the second sliding surrounding surface 109A of the main body 102 is arranged. The second valve body 125 is cylindrically formed and provided with a second valve seating surface 125A having a tapered surface in the internal surrounding surface of one end portion of the second valve body 125. Also, an end of a solenoid rod 151 is connected to a fitting hole provided with a plurality of passages 125C along the surrounding surface of the other end portion of the second valve body 125. Both ends of the solenoid rod 151 are slidably introduced by a first bearing 154A and a second bearing 154B. Then, the solenoid rod 151 is operated according to the magnitude of electrical current flowing in the solenoid 150 to open or close the second valve seating surface 125A of the second valve body 125 with regard to the second valve surface 120B.
The operation of thus-constituted pressure proportional control valve 100 is initiated by closing the first valve surface 120A of the first valve body 120 with regard to the first valve seating surface 110B due to elasticity of the first spring 140A. Then, the working fluid running in from the input port 105 is blocked by the closing of the first valve surface 120A. Also, when the solenoid 150 works, the second valve surface 120B of the first valve body 120 and the second valve seating surface 125A of the second valve body 125 are jointed to close, and the first valve surface 120A of the first valve body 120 is separated from the first valve seating surface 110B to open. By the opening of the first valve surface 120A, the working fluid running in from the input port 105 runs out into the second communication chamber 103B. Note that in the opening/closing shown in FIG. 5, the first valve body 120 and second valve body 125 are opened, so that the working fluid runs out from the output port 106 to the discharge port 107.
Then, in the pressure proportional control valve 100, the first valve body 120 is opened/closed by sliding its outer circumference surface 120C and the first sliding surrounding surface 108A, and also slides while the first seal ring S1 provided between the sliding surfaces and the outer circumference surface 120C strongly friction. Therefore, the first valve body 120 has large sliding resistance during the opening/closing. Particularly, when the pressure of the working fluid is high, the first seal ring S1 is radially extended by this pressure to be elastically deformed, so that the first seal ring S1 slides while strongly frictioning with the cohesive first valve body 120. Therefore, the sliding resistance of the first valve body 120 becomes large, causing to lower the response performance of the opening/closing of the pressure proportional control valve 100.
Also, the outer circumference surface 120C of the first valve body 120 slides with the first sliding surrounding surface 108A. The working fluid intrudes between the sliding surfaces, so that external impurities included in the working fluid may intervene between the sliding surfaces. Therefore, the first valve body 120 pressed by the first spring 140A in which the force changes depending on the displaced position may cause delayed response during the operation. Further, this first valve body 120 is pressed to one surface, possibly causing stick phenomenon (so-called hydrolock) between the sliding surfaces. As a result, operation property of the pressure proportional control valve 100 is changed to increase hysteresis phenomenon in the relation between the pressure and amount of flow of the working fluid. Further, the constitution to simultaneously slide the first valve body 120 along to two distant axes of the first sliding surrounding surface 108A and the first valve bore surrounding surface 110A elevates the costs of assembly and processing.
Further, there is a solenoid valve as shown in FIG. 6 as a related art of the present invention (e.g. Japanese Unexamined Patent Publication 2002-295708 (Patent Document 2)). FIG. 6 shows a structure in which a valve portion 210 and a solenoid 230 are integrated. In this valve portion 210, a valve sleeve 211 is internally provided with a through-hole 211A. The through-hole 211A of the valve sleeve 211 is partitioned by a first valve seat 212, a second valve seat 213 and a screw 214 to form an inflow chamber 215A, a pressure controlling chamber 215B and an outflow chamber 215C. To the inflow chamber 215A, an inflow port 215A1 communicates. Also, to the pressure controlling chamber 215B, a pressure controlling port 215B1 communicates. Further, to the outflow chamber 215C, an outflow port 215C1 communicates.
Also, a first valve body 216A is placed in the inflow chamber 215A. The first valve body 216A is elastically pressed by a spring 219 to contact and discontact with a first valve seating surface 212A of the first valve seat 212, so that a first poppet valve is constituted. The first poppet valve is opened/closed by an interacting force between the solenoid 230 and the spring 219 to open/close a passage between the inflow chamber 215A and the pressure controlling chamber 215B. Also, a second valve body 216B is placed in the pressure controlling chamber 215B. Then, the first valve body 216A and the second valve body 216B are connected via a connecting portion 216C to constitute a connecting valve body 216 as a whole. The second valve body 216B contacts and discontacts with a second valve seating surface 213A of the second valve seat 213 to constitute a second poppet valve. The second poppet valve is opened/closed by an interacting force between the solenoid 230 and the spring 219 to open/close a passage between the pressure controlling chamber 215B and the outflow chamber 215C.
Thus-constituted valve portion 210 works as with the above-described pressure proportional control valve 100. And, according to the magnitude of electrical current flowing in the solenoid 230, the first poppet valve and the second poppet valve are opened/closed to control the working fluid. On the other hand, the pressure of the working fluid flowing from the inflow port 215A1 into the inflow chamber 215A is pressed to transport by a pump, so that the working fluid may pulse (fluctuate). The pulsing pressure flowing in from the inflow port 215A1 works on the connecting valve body 216, which may cause the connecting valve body 216 to pulse since the connecting valve body 216 is not constituted to cancel the pressure worked on its both sides to the pressure of the working fluid. Therefore, it may be difficult that the first poppet valve and the second poppet valve control the working fluid properly.    [Patent Document 1] Japanese Unexamined Patent Publication No. 2004-197858    [Patent Document 2] Japanese Unexamined Patent Publication No. 2002-295708